1. Technical Field
The present disclosure relates to an on-vehicle power generation control unit and, more particularly to a power generation control unit that controls power generator mounted on vehicles such as cars and trucks.
2. Description of the Related Art
Generally, maximum output current of the on-vehicle power generator increases when the rotational speed of the power generator becomes higher. Hence, when a large size body is employed for the on-vehicle power generator in order to secure sufficient output power at low rotational speed region, the maximum output current increases at high rotational speed region as well. As a result, since it is necessary to use a charge line having thick cable dimension and a fuse having large current capacity, manufacturing cost and weight of the on-vehicle power generator increases.
As a conventional technique to deal with above-described situation, for example, Japanese Examined Patent Application Publication No. 1994-38720 discloses an on-vehicle power generator in which the excitation current is controlled to be below a predetermined value so that the output current is suppressed. In this type of on-vehicle power generator, a limit value of the excitation current is set so as to obtain predetermined output characteristics when the temperature of the on-vehicle power generator increases to be more than the predetermined value.
Moreover, in recent years, an on-vehicle power generator in which the upper limit value of the excitation current can be set by communicating with the vehicle ECU (electronic control unit) has been developed. In this case, the vehicle ECU transmits a command to control the on-vehicle power generator such that the output power or the output torque of the on-vehicle power generator can be controlled in response to a state of load of the engine or etc, by the command transmitted by the vehicle ECU.
In the on-vehicle power generator disclosed in the above-described patent document, since the on-vehicle power generator suppresses the output current by itself, a problem arises that the on-vehicle power generator cannot perform temporary limiting of the output power (e.g. power generation suppression when the engine starts) based on a request by an external equipment such as a vehicle ECU
Meanwhile, in a case where the on-vehicle power generator communicates with the vehicle ECU so as to variably set the upper limit value of the excitation current, thereby controlling the output power of the on-vehicle power generator, the output power can be temporarily limited by setting the upper limit of the excitation current corresponding to the target maximum output current based on the command transmitted by the vehicle ECU.
However, setting the upper limit of the excitation current is determined by cable dimension of the charge line or allowable current capacity of the fuse so that the upper limit of the excitation current needs to be changed depending on the electrical load which varies depending on grade of the vehicle even in the same type of vehicle or, depending on size (characteristics) of the power generator. Therefore, a problem arises that a plurality of vehicle ECUs corresponding to the respective vehicles should be prepared in the power generation control unit.